1. Field of the Invention
The present invention relates to a sintered oil-impregnated bearing for rotatably supporting a motor shaft or the like, and a motor using same. More particularly, the present invention relates to the material technology for improving the lubricant performance of a sintered oil-impregnated bearing.
2. Related Art
As a bearing device for rotatably supporting a shaft of a motor or the like, there is known a structure having two sintered oil-impregnated bearings each having a shaft hole at the center, disposed one on the other in the axial direction in a bearing holder.
This sintered oil-impregnated bearing is manufactured by first molding composite fine particles comprising iron powders having surfaces coated with copper into a cylinder shape, sintering this cylindrical mold at a temperature near 800.degree. C., and impregnating lubricant oil into the sintered body formed by the sintering.
In the sintered oil-impregnated bearing as mentioned above, even if the sintered body is impregnated with lubricant oil, a boundary lubrication condition may occur, wherein a motor shaft and the sintered body are in direct contact with each other between the motor shaft and the sintered oil-impregnated bearing, if a large eccentric load is applied in a lubricant oil lacking state when used in a motor operable in a wide rotational speed range of, for example, 200 rotations per second to 6000 rotations per second, such as a spindle motor for driving a CD-ROM, and if a motor having a large side thrust load such as a capstan motor for VTR rotates at a low speed in a high temperature range or at a high speed in a low temperature range to cause a large load thereto. Of course, if lubricant oil is completely exhausted in a sintered oil-impregnated bearing, this causes the above-mentioned boundary lubrication condition. However, a conventional sintered oil-impregnated bearing has a problem in that the above-mentioned boundary lubrication condition leads to abrasion and/or seizure in a relatively short time in the sintered oil-impregnated bearing, since a material itself composing the sintered body does not provide any lubricating action.